Table saws are power tools used to cut work pieces of wood, plastic and other materials. Such saws are among the most widely used power tools in woodworking and materials processing shops, carpentry and building work sites. Four general classes of table saws are in common use including bench top table saws, contractor table saws, cabinet table saws and hybrid table saws.
A table saw includes a flat surface, or table, with a circular saw blade extending vertically up through a slot in the table. The saw blade is mounted on an arbor which is driven by an electric motor (directly, by belt, or by gears). The saw operator slides a workpiece on the table against and past the blade while the circular blade revolves at a high rate of speed (typically about 4,000 rpm) and cuts through the workpiece. The thickness of the workpiece that can be sawed completely through, or the depth of the cut into the workpiece, is controlled by moving a saw motor trunnion or carriage, holding the motor, saw arbor and saw blade, up or down, relative to the saw table top. The higher the blade protrudes above the table, the deeper the cut that is made in the workpiece. Most often the cut into the workpiece is made perpendicular to the saw table but most table saws also can be adjusted to make cuts at angle of up to 45 degrees from the perpendicular. Such angle or bevel cuts are made by rotating the saw motor carriage from the perpendicular such that the angle of the motor, blade arbor and blade are adjusted to provide the desired cutting angle.
Table saws are generally designed to allow rotation of the carriage, motor, arbor and blade either to the left or to the right (but not both).
Table saws typically are provided with various pieces of auxiliary equipment including a rip fence to guide a workpiece, make rip cuts, that is to cut work pieces generally with the grain of the wood, and a miter gauge to cut work pieces perpendicular to, or generally at an angle to, the grain. When a saw cuts into a piece of wood or other workpiece, the removal of material leaves a void called the “kerf.” A splitter, a vertical projection located (relative to the saw operator) behind the saw blade, is provided as a required safety attachment for all table saws currently sold in the United States. The splitter is typically either a pin or a fin-shaped metal plate, and is intended to fit within the generally narrow material-void or saw-kerf formed directly behind the saw blade during cutting operations. The splitter is typically slightly narrower in width than the saw-kerf and is aligned directly in line with the saw-kerf and is intended to prevent the cut in the wood from closing, thereby pinching the back of the blade and kicking back the workpiece toward the operator. In addition to the splitter, table saws are also typically provided with an anti-kickback device that most often consists of serrated or toothed anti-kickback pawls as well as a clear plastic blade cover. The use of a typical saw blade guard pivotally supported by a splitter is shown in U.S. Pat. No. 6,578,460 issued to SARTORI. Table saws also have an easily removable insert closely surrounding the blade in the table top. The insert is removable, in order to access the saw blade for blade changing. For example, one may wish to swap out a blade which has become dull, and replace it with a sharper blade.
Of the many power tools used in a typical woodworking shop, table saws present perhaps the greatest risk of injury. Table saws present a very serious risk of injury or impairment of health to operators in several ways. A high risk of trauma injury to the operator exists because the operator is often exposed to the saw blade, which is spinning at about 4,000 rpm when in use. The blade is designed to cut through hard materials such as wood, cuts very quickly through human flesh and can sever a finger, several fingers or an entire hand upon the operator's slightest slip or inadvertent misplacement. Second, table saws are prone to sudden “kickback” of the work piece. This occurs when the blade lifts the workpiece off the table and hurls the workpiece backward (opposite to the direction of workpiece feed), at a high velocity, in the direction of the operator. It is not uncommon for a kicked-back workpiece to have sufficient velocity to become embedded in a wall or to cause trauma injury to the operator. Serious injury can also occur from kickback if the operator is struck in the face or the eye.
Safety features or systems have been developed to minimize the risk of injury to saw operators. Probably the most common saw safety feature is a blade guard that physically blocks a user from making contact with the spinning blade. Prior art blade guards have been designed to be pivotally attached to a splitter as shown in U.S. Pat. No. 2,786,496 issued to ESCHENBURG and U.S. Pat. No. 4,625,604 issued to HANDLER. Prior art blade guards have also been designed to be pivotally attached to an overhead arm which is supported by a vertical column that may either be attached to the saw or that may be free-standing as shown in U.S. Pat. No. 3,105,530 issued to PETERSON and U.S. Pat. No. 7,000,515 issued to JORGENSEN. Neither of these prior patents provide the important fixed hold-down safety capability of the present invention and they suffer from other shortcomings as well. While prior art blade guards may effectively reduce the risk of injury, it is well known in the woodworking field that the most common types of prior art blade guards, more often than not, are removed from the table saw altogether. The widespread perception is that such devices are cumbersome and interfere with the operation of the saw in many situations. Also, there are instances where the nature of the sawing operation to be performed precludes using a prior art guard, such as when making non-through cuts such as grooves or dado cuts. The guard must be easily removed to facilitate such special cuts and often the operator fails to reinstall the blade guard after the special cut is completed. As a result, many injuries occur each year when saws are operated without a blade guard being properly in place.
At least one recent saw safety system, as shown in U.S. Pat. No. 6,994,004 issued to GASS, has been developed that does not entirely rely on such guards, but instead detects contact of the operator's body with the saw blade. An electrical signal is applied to the saw blade and any contact of the operator with the blade causes a sudden change in the electrical characteristic of the applied signal and is immediately detected by a monitoring circuit. The monitoring circuit rapidly triggers release of a spring which forces a metal block into the teeth of the spinning blade, quickly stopping it and destroying the saw blade and metal block assembly. While this system offers an important improvement in table saw safety, it is not without drawbacks. The device is only available with the purchase of saw models having the safety feature built-in; it cannot be retrofitted onto existing table saws. The system is said to be subject to false triggering and each such event destroys both the saw blade and the fused spring release module both of which are costly to replace and require the saw to remain without the safety feature until the parts are replaced. U.S. Pat. No. 7,290,474 issued to KELLER also offers a destructive method of stopping a table saw blade.